Pneumatic system for a rotary hammer device



Dec. 17, 1963 J. MccLouD 3,114,421

PNEUMATIC sYsTEM FOR A ROTARY HAMMER DEVICE Filedv April 4, 1960 2 Sheets-Shea?l 1 W Q A w gg q@ @QR YA- N Q .21 @A f s Q Q Q E Q3 gi R A---f 1 UQQQ n A Q @u -q A A A A l m3 A A 1 l W f); 1 Q @Q @zx l, m il" N 9 :I i t g @A A mmvron E Jame/VCCZOLMZ,

ES BY Q MWF/fm Dec. 17, 1963 J. MocLouD 3,114,421

PNEUMATIC SYSTEM FOR A ROTARY HAMMER DEVICE 2 Sheets-Sheet 2 3,114,421 PNEUMATEC SYSTEM FR A ROTARY HAMMER DEVECE f .lames McCioud, Glenview, Hi., assigner to Skil Corporation, (hicago, iii., a carporation oi Delaware Filed Apr. 4, 1960, Ser. No. 19,784 13 Claims. (Cl. 1661-138) The present invention relates to improvements and innovations in a hand operable rotary-hammer device, and more particularly to a pneumatic system adapted to provide the hammering action in such a device.

It is an important object of the invention to provide a pneumatic system for a rotary-hammer device which selectively provides either a combination rotary and hammering action or separate rotary and hammering actions.

A more detailed object of the invention is to provide a new and improved rotary-hammer device wherein tool means mounted therein may be provided with a rotary action as a result of being drivingly engaged in the end of a rotary cylinder and wherein the tool means may also be provided with a hammer-like action as a result of impact engagement therewith by a striker member reciprocal by pneumatic means in the rotary cylinder.

Another object of the invention is to provide a new and improved rotary-hammer device of the character described wherein the pneumatically reciprocal striker member is automatically rendered inoperable when tool means adapted for rotary movement only are mounted in the device whereby to prevent unnecessary wear of the parts.

Further objects of the invention are to provide a new and improved rotary-hammer device of the character described which may be readily operated by one person, which is rugged and requires little or no maintenance, and which includes a self-cleaning feature for the pneumatic system as a result of the rotary action of the cylinder which centrifugally tends to maintain the interior of the cylinder in which the striker member is reciprocal free of dust and other harmful particles.

Certain other objects of the invention will, in part, bev

obvious, and will in part appear hereinafter.

For a more complete understanding of the nature and scope of the invention reference may now be had to the accompanying drawings wherein:

FIG. l is a generally longitudinal vertical section taken through a rotary-hammer device embodying the invention and showing a tool adapter element designed for a combined rotary and hammering action mounted in the device; Y

FG. 2 is a fragmentary vertical section of the nose portion of the rotary-hammer device of FIG. 1 showing a tool adapter element designed for rotary movement only, mounted in the device; and

FIGS. 3, 4, 5 and 6 are a series of fragmentary horizontal sections illustrating various positions of the piston members reciprocal in the rotatable cylinder.

As illustrated in FIG. l, a rotary-hammer device embodying the invention is provided with a multi-part housing including a tool-supporting portion 12, a powerunit-supporting portion 13, and a gear-housing portion 14 which interconnects the portions 12 and 13. A suitable handle 15 is secured between the housing portions 13 and 14.

A tube or cylinder 26 having a bevel gear 24 secured about one end thereof and a tube insert 27 secured in its other end is rotatably mounted in the housing portion 12 by suitable rear and front bearings 19 and 22,

respectively. The tube insert 27 is provided with a through bore 3d having a tool element drive member 32 secured therein. The drive member 32 is provided with an axial through bore having an oetagonal formation 33 at its inner end and an internal thread 37 at its outer 3,ll4,42l Patented Dec. 17, 1963 end. A collar-like nose member 38 is mounted on the outer end of the housing portion 12 and has a cylindrical nose insert member 41 press fitted therein. An annular or ring-like guide member 44 is press fitted into the inner end of the bore of the nose insert member 41 and is provided with an internal octagonal formation 45 for a purpose to be described.

Suitable tool means, such as various tool adapters or one-piece tool elements, designed for either combination rotary and hammering actions or separate rotary or hammering actions are adapted to be mounted in the nose end of the rotary-hammer device 10. In FIG. l, a tool adapter 46 adapted for a combination rotary and hammering action is shown mounted in the device 10. The elongated adapter 46 includes a long shank portion 47 which extends rearwardly through the drive member 32 and projects into the cylinder 26 beyond the inner end of the tube insert 27. An enlarged body portion 43 of the adapter 46 is provided with an outwardly dared shoulder 453 which is engageable with the outer end of the drive member 32 when the adapter 46 is in its innermost or rearmost position. The outer end 50 of the adapter 46 is reduced in diameter and provided with a taper whereby to permit the mounting thereon in the usual manner of tool elements adapted for a combination rotary and hammering action, such as percussiontype drill bits.

The shank portion 47 of the adapter 46 is provided with an octagonal formation 51 for both rotary driving, and reciprocal sliding interengagement within the Octagonal formation 33 in the bore of the drive member 32 whereby the adapter 46 is not only reciprocally slidable relative to the nose of the rotary-hammer device 10 but is also rotatable with the cylinder 26. An adapter lock member 52, which is mounted on the nose end of the rotary-hammer device 1d, is provided at its outer end with an inwardly flanged or counter-bored sleeve portion 54 for guiding engagement with the body portion 43 of the adapter 46. The counter-bored sleeve portion 54 also serves to limit outward movement of the tool adapter 46 as a result of engagement therewith of the outwardly flared shoulder 49 on the tool adapter 46.

A tool adapter designed for hammering action only would be similar in design to the tool adapter 46 but would be provided with a smooth shank, rather than the octagonal formation 51 for rotary driving engagement with the drive member 32. Such an adapter, which would be adapted for use with non-rotary hammering tool elements, such as chisels and star drills, would preferably be provided with an octagonal formation on its main body portion for slidable engagement with the octagonal formation 45 of the guide member 44 whereby to insure non-rotation thereof.

To provide a hammer-like action for tool elements mounted in the device 16 and having long shank portions projecting into the cylinder 26, such as the tool adapter 46, a free piston or striker member 5S provided with a ring 61 is mounted in the cylinder 26 for reciprocation therein. The striker member 58 is provided on its leading or front face with a recess 59 in which is secured a striker button 6@ formed of a material adapted for striking engagement with the inner end of a lonk shank tool element such as the adapter v46.

In FIG. 2, a rotary but non-hammering tool element in the form of a conventional drill chuck is shown mounted in the nose end of the device 10 whereby to provide purely rotary actionv of a non-percussion-type drill bit mounted therein. The drill chuck 129 is provided with a cylindrical shank portion 121 having its inner end eX- ternally threaded for threaded engagement with the internal thread 37 formed in the outer end of the bore of the drive member 32. There is no engagement of the 3,1 shank portion 121 with the internal octagonal formation of the guide member 44 to hinder rotation thereof. No portion of the short shank tf1 of the drill chuck i2@ projects into the cylinder 26, thus eliminating the possibility of any impact engagement therewith by the striker member 5S upon reciprocation thereof. Thus, during operation of the device li@ the drill chuck l2@ is rotated through its driving engagement with the rotating cylinder 26, but is not reciprocated.

The invention is primarily concerned with a novel pneumatic system for reciprocating the striker member 58 in the rotating cylinder 26 whereby to impart a hammer-like action to long shanked tool elements, such as the adapter IE6, which are mounted in the rotary-hammer device 1). As will be described in detail herein, the striker member 5S is pneumatically actuated with a reciprocating movement in response to reciprocating movement of a power driven piston 64 in the inner end of the cylinder 26. The piston 64 is reciprocated by a driven crank arm or pitman rod 65 which is pivotally connected to the piston 64 by a dowel pin 66 which extends through aligned bores formed in the end of the crank arm 65 and in guide bushings 67 mounted in the piston 64. The piston 6dis provided with suitable rings The reciprocal power piston 6d and the rotatable cylinder 26 are both driven by an electric motor 70 which is mounted by suitable fastening means in the housing portion t3 and which has a vertically disposed drive shaft 7 1. The lower end of the d `ive shaft 71 is rotatably supported in a bearing 72 and the upper end extends into the housing portion i4 and is rotatably supported in a bearing 73. Preferably, a fan blade 7d is mounted on the drive shaft '71. The power circuit for the electric motor is a standard-type circuit well-known in the art and is therefore not shown and described in detail herein. A power cord 75 and an on-and-off switch controlled by a trigger-like member 76 carried on the handle 15 are provided for the power circuit.

Suitable motion transmitting drives are provided between the drive shaft 71 or" the motor 7@ and both the rotatable cylinder 26 and the power piston 64. The upper end of the drive shaft 71 is provided with a gear tooth formation 7 S which is meshed in driving engagement with gear teeth 79 formed on a gear '77 integrally formed on a shaft Sti, which shaft is rotatably supported in bearings S1 and 84. The gear '77 is provided on its upperface with an upstanding post SZ which is arranged eccentrically thereon relative to the axis of rotation of the shaft 30. The opposite end of the crank arm 65 from the piston 64 is bored whereby to permit rotatable mounting thereof on the upstanding post SZ by means of a suitable bearing 33. Thus, during operation of the motor 7@ the piston 64 is reciprocated in the inner end of the cylinder 26 in a manner well-known in the art.

A pinion gear 86 which is keyed to the lower portion of the shaft Sti meshes with a pinion gear 7 which is keyed to the lower end of a shaft SS which is supported in bearings 89 and 96. A bevel gear formation 9?. is provided on the upper end of the shaft 88 in meshing engagement with a gear formation 2.5 on the bevel gear 24. Thus, the cylinder 26, which is driven by the motor 7@ through the described gear train, is simultaneously rotated as the piston 64 is reciprocated therein.

Suitable porting is provided in the cylinder 26 for the pneumatic actuation of the striker member 53. A plurality of exhaust ports are formed in the outer end of the cylinder 26 adjacent the inner face of the tube insert 27. The ports 95 communicate with an annular manifold space 96 defined between the outer surface of the cylinder 26 and the inner surface of the housing EZ. The manifold space 96 is in communication through an opening 9S with an air channel 97 which is open at its rear end to atmosphere. Thus, during the forward or working stroke of the striker member 5S, the air disposed forwardly thereof in the cylinder 26 is evacuated or exhausted to atmosphere Cil l with minimum restriction to the tlow thereof through the ports 95, the manifold space 96, the opening 98 and the air channel 97. l

The pneumatic operation of the rotary-hammer device i@ may best be described with reference to FIGS. 3-6. in FIG. 3, the striker member 53 is shown at its impact point with the inner end of a long shank tool means such as the tool adapter F56. The power piston 6L? is then at the forwardmost point of its working stroke. As the power piston 64 moves rearwardly, a vacuum is created in space between the piston 64 and the striker member 5S, which vacuum acting on the rear face, in combination with atmospheric pressure acting on the leading face, of the striker member 58 iv ates rearward movement of the striker member 5S in the cylinder 26. As the piston 64 slows down as it reaches its rearwardmost position (FXGS. 4 and 5), reverses itself, and begins its forward stroke, the striker member 5d continues its rearward movement due to the momentum thereof. Thus, the air trapped between the striker member 58 and the piston 64 becomes highly compressed to create a tremendous pressure between the two piston members. This pressure serves both as an air cushion preventing contact of the striker member 5S with the piston 64 and as the driving force that reverses the striker members direction and propels it forwardly toward the nose end of the cylinder at a very high velocity whereby to deliver a sharp impact blow to the inner end of the long shank tool means projecting into the cylinder 26. It has been determined that the forward or working stroke of the striker member 53 is initiated at approximately the instant that the power piston 64- has completed approximately two-thirds of its forward stroke, as graphically illustrated in FIG. 6.

Due to the extreme pressure developed between the striker member 53 and the piston 64 during the working stroke thereof, some of the air trapped therebetween may be forced past the striker member 58. A substantial evacuation of air from the space between the striker member 58 and the piston 64 in this manner would result in the formation of a vacuum interlock between the striker member 53 `and the piston 64. A venting port 160 is provided to prevent the development of such a vacuum interlock. The port 1%, which is relatively small, is formed in the cylinder 26 adjacent to and forwardly of the forwardmost position of the leading face of the piston 64 (FG. 3). Thus, during the rearward stroke of the piston 64 sul'licient air may be drawn into the cylinder 26 through the venting port Mii to compensate for any air .lost during the forward stroke of the piston 64. When the compression in the space between the striker member 58 and the piston 64 is at its maximum, the port 106 is covered by the striker member 53, as illustrated in FIG. 6, whereby to prevent any pressure loss through the port Miti. The size of the port is critical for proper pneumatic operation of this system and to prevent a vacuum interlock between the two piston members. The size of the port T00 is selected to provide a proper impedance match for the power requirements of the particular rotary-hammer device. For example, with a cylinder Z6 having an inner diameter of 21/2 inches, the diameter of the port N9 should be Mp, of an inch.

During operation of the rotary-hammer device l0 when a non-hammering, short shank tool means, such as the drill chuck T29, is mounted in the device llt), the striker member 53 would normally be reciprocated with impacting engagement against the inner end of the tube insert member 27 inasmuch as no shank portion of the tool means projects into the cylinder 25 for impacting engagement by the striker member 58. To eliminate unnecessary wear of the parts in this situation, means are provided `for rendering the striker member 5S inoperable when `a short shank tool means is mounted in the device liti. As best illustrated in FIGS. l and 2, a series of vacuum-counteracting ports 124 of substantial diameter is formed in the cylinder 26 rearwardly of the forwardmost position of the rear face of the striker member 53, as when the striker member 58 is in abutting engagement with the-inner end of the tool insert member 27 when a short shank -tool means, such as the drill chuck 120, is mounted in the device 10, and forwardly of the forwardmost position of the rear face of the striker member S when a long shank tool mea-ns, such as the tool adapter 46, is mounted in the device lit. The ports 124 are open to atmosphere through the manifold space 96 and the air channel 97. As a result of the exposure of the ports i24- to the space between the striker member 53 and the power piston 64 when the striker member 58 is advanced past its normal impact point into engagement with the inner end of the tube insert member 27, as when Ia short shanked tool means is mounted in the device i0, rearward movement of the power piston 64 is ineffective to create a vacuum in the space between the piston 64 and the striker member 58. Thus, with no pressure differential on opposite ends of the striker member 53 there will be no rearward movement of the striker member 5S during reciprocation of the power piston 64 and, thus, no unnecessary reciprocation of the striker member 5S when a non-hammering tool means is mounted in the device lt for rot-ary movement only.

It is noted that the rotation of the cylinder 26 provides a centrifugal action which effectively serves to maintain the interior of the pneumatic cylinder 26 free of dust and other particles which would be harmful to proper operation of the pneumatic system.

lt will be understood that certain changes may be made in the construction or arrangement of the pneumatic system for a rotary-hammer device disclosed herein without departing from the spirit and scope of the invention as defined in the appended claims.

I claim:

l. In a power hammer device, a cylinder having a power piston reciprocal in one end thereof and a working tool element attached to the opposite end thereof, said cylinder having exhaust port means in said opposite end thereof, a free pist-on in said cylinder adapted to impart Ia hammer-like action to said working tool element, which free piston is adapted to be pneumatically reciproc-ated during reciprocatio-n of said power piston due to the alternate development of high and `low pressures in the space between said pistons during respective inward and outward strokes of said power piston relative to said cylinder, said cylinder having a relatively small vent port formed inthe wall thereof adjacent to and inwardly of the innermost position of said power piston, said vent port being open to atmosphere to prevent the creation of a vacuum Ainterlo-ck between said pistons by permitting, during the outward stroke of said power piston, the intake of suicient air into the space between said pistons to compensate for any air lost past said free piston during the inward stroke of said power piston, said venting port being closed from the atmosphere by said free piston only after said power piston has started its inward stroke whereby to permit the development of a nal maximum compression force between said power and free pistons.

2. A rotary-hammer device comprising, in combination, a rotataby mounted cylinder, tool holding and driving means associated with one end of said cylinder, a long shank tool element mounted in said tool holding and driving Imeans and having its shank portion extending into said one end of said cylinder, a piston-like striker member wholly within said cylinder, exhaust porting means formed in said one end o=f said cylinder, a piston reciprocal wholly within the other end of 'the cylinder and adapted for pneumati-cally reciprocating said striker member into impacting engagement with the shank of said long shank tool element mounted in said tool holding and driving means, venting port means formed in said cylinder just inwardly of the innermost position of said piston,V power means operably connected to simultaneously reciprocate said piston and rotate said cylinder, and

control porting means formed in said cylinder outwardly of the inner surface of said striker member when in impacting engagement with the shank of said long shank tool element, said control porting means serving to render said striker member inoperable when no long shank tool element is mounted in the device.

3. A rotary-hammer device comprising, in combination, a rotatably mounted cylinder, tool driving means secured in the forward end of the cylinder for rotary movement therewith, tool means mounted in said device and having Ian inner end extending through said tool driving means and into the forward end of said cylinder, a piston-like striker member movable in the cylinder, exhaust port means opening to atmosphere formed in the forward end of the cylinder, a power piston mounted for reciprocal movement in the rear end of the rotatable cylinder, power means oper-ably connected for rotating said cylinder `and simultaneously reciprocating said power piston with rearward movement of said piston creating a vacuum behind said striker member and initiating rearward movement thereof with said rearward movement continuing after `said power piston has begun its forward stroke whereby the air disposed therebetween is so highly compressed that it effectively reverses the direc- -tion of movement of said striker member and actuates it forwardly at a high velocity to tdeliver 'a sharp impact lblow to 'the inner end of said tool means protecting into the forward end of the cylinder, and a small venting pont open to atmosphere formed in the cylinder, said venting port being located adjacent to and forwardly of the forwardmost position of said power piston whereby any air forced past said striker member `during the forward stroke of said power piston is replaced through said venting port during rearward movement of said power piston, said venting port remaining open until after said power piston has begun its forward movement when it is then covered by said striker member to permit the development of a maximum compressive force between said power piston and said striker member.

4. In the combination recited in claim 3, vacuumcounteracting port means opening to atmosphere formed in said cylinder, said vacuum-counteracting port means being spaced 'la greater distance from the forward end of said cylinder than the longitudinal length of `said striker member whereby to effectively prevent the development of a vacuum behind said striker member upon rearward movement of said power piston when the striker member is disposed forwardly of said vacuum-counteracting port means as a result tof advancing past its normal impact point when no tool means projects into the forward end lof the cylinder for impact engagement by said striker member.

5. In la power device adapted for imparting a reciprocal, hammer-like laction to tool elements mounted therein, a cylinder, la piston reciprocal in the rear end thereof, tool element holding means associated with the front end of said cylinder for supporting tool means in the device, a long shank tool element mounted in said holding means with the shank end extending into the front end tof said cylinder, exhaust port means at the front end of said cylinder opening to atmosphere, a pistonlike striker member pneumatically reciprocal in said cylinder for impact engagement with the shank end of said long shank tool element for imparting a hammerlike `action thereto, the rearward 'stroke of said striker member being initiated lby a vacuum 'of less than atmospheric pressure being created rearwardly thereof during rearward movement of said piston wit'h the rearward movement of said striker member continuing after said piston has started its forward stroke whereupon the air disposed therebetween is highly compressed and serves to initiate a powerful forward stroke of said striker member into impact engagement with the shank end of the long shank tool element, the air disposed forwardly of said striker member being evacuated to atmosphere through said exhaust ports during the forward stroke of d said striker member, and a small vent port open to atmosphere formed in said cylinder adjacent to and forwardly `of the forwardmost position of said piston, suicient air being drawn into the space between said striker member and said piston through said vent port during trie rearward stroke of said piston to compensate for any air lost past said striker member during the forward stroke of said piston whereby to prevent the development of a vacuum interlock between said striker member and said piston, said vent port being covered by said striker member only after said piston has started its forward stroke whereby a final maxim-um compression force is developed between said piston and said striker member to initiate said powerful forward stroke of said striker member.

6. A power device as recited in claim wherein vacuum-counteracting ports opening to atmosphere are formed in said cylinder, said ports being normally closed by said striker member in its forward position during impact engagement with the shank end of said long shank tool element mounted in the `device with said ports being opened to the space between said striker member and said piston when said striker member is permitted to advance forwardly beyond its normal impact point when no shank end of a tool element projects into said cylinder whereby to prevent the development of a vacuum rearwardly of said striker member during the rearward stroke of said piston, thus rendering said striker member inoperable.

7. In a power device, fa cylinder, a power piston reciprocal in the rear end thereof, exhaust port means formed in the front end of said cylinder, `a free piston in said cylinder, control port means formed in said cylinder, said control ports being positioned a distance from the front end of the cylinder somewhat greater than the corresponding longitudinal dimension yof said free piston whereby when said free piston is `disposed `against the front end of said cylinder said control ports are open to the space between said pistons, `abutment means selectively insertable into the front end of said cylinder to limit forward movement of said free piston to a point wherein said control ports are not open to the `space between said pistons whereby to permit the development of a vacuum between said piston members during rearward movement of said power piston whereby to initiate like movement ot' said free piston, said movement of the free piston continuing even after said power piston begins its forward stroke whereby a high compressive force is ideveloped between said pistons which serves to initiate a forward power stroke of said free piston, and a small vent port formed in said cylinder in a position whereby it is open to the space between said pistons during rearward movement of said power piston and is covered by said free piston after said power piston has begun its forward movement to develop said high compressive force between said pistons, said control port means when open to the space between said pistons being effective to prevent the development of a vacuum between said pistons during rearward movement of said power piston and, thus, render said free piston inoperable.

8. In a rotary-hammer device having a rotatable cylinder, tool driving means secured in the forward end of the cylinder, and power means operably connected for rotating the cylinder, the improvement which comprises, tool means mounted in the device and having an inner end extending through said tool driving means into the forward end of said cylinder, a pair of pistons disposed wholly within the rotatable cylinder one of which is operably connected to the power means for positive reciprocation in the rear end of the cylinder and the other of which is adapted to be pneumatically reciprocated in the cylinder as a result of reciprocation of said one piston whereby to impart a hammer-like `action to the inner end of said tool means extending through the tool driving means and into `the cylinder as a result of impact engagement therewith, exhaust port means formed in the cylinder forwardly of the impact point of said other piston for exhausting air during the forward stroke of said other piston, rearward movement of said one piston creating a vacuum between the two pistons which serves to initiate the rearward stroke of said other piston, which piston continues its rearward movement after said one piston starts its forward movement with the high compressive force developed therebetween serving to initiate a powerful forward stroke of said other piston into impacting engagement with the tool means, and a venting port open tto atmosphere formed in said cylinder adjacent to and forwardly of the forwardmost position of said one piston whereby to permit a small quantity of air to be drawn into the space between the two pistons during the rearward stroke of said one piston -to compensate for any air forced past said other piston during the forward stroke of said one piston, said venting port being small enough that it causes no detrimental reduction in the vacuum developed between the two pistons during the rearward stroke of said one piston, said venting port being covered by said other piston after said one piston begins its forward stroke to permit the development of a maximum compressive force therebetween.

9. The improvement in a rotary-hammer device recited in claim 8 wherein vacuum-counteracting port means opening to atmosphere are formed in the cylinder rearwardly of the forwardmost possible position of said other piston in the cylinder whereby to prevent the formation of the vacuum normally developed during the rearward stroke of said one piston and thus effectively prevent reciprocation of said other piston when there is no tool means having an inner end extending into the cylinder mounted in the ldevice whereby said other piston is permitted to advance to its forwardmost possible position in said cylinder.

l0. In a rotary-hammer device having a rotatable cylyinder, tool driving means secured in the outer end of the cylinder for rotary movement therewith, and power means for rotating the cylinder, ythe improvement which comprises, tool means mounted in the device and having an inner end projecting through the tool idriving means and into the outer end of ythe cylinder, a power piston mounted for reciprocal movement in the inner end of the rotatable cylinder, power means for reciprocating said power piston, a piston-like striker member freely movable in the cylinder, port means in the outer end of Ithe cylinder and open to atmosphere, whereby inward movement of said piston creates a vacuum behind said striker member causing it to follow Said power piston whereby after said piston begins its outward stroke the air disposed therebetween is compressed sufliciently to serve as a driving force for reversing the direction of movement of said striker member and actuating it outwardly at a high velocity to deliver a sharp impact blow to the inner end of said tool means projecting through the tool driving means and into the outer end of the cylinder, and a small venting port in :the cylinder open to atmosphere, said venting port being located just outwardly of the outermost position of the outer face of said power piston whereby any air lost past said striker member during the outward stroke of said power piston may be replaced through said venting port `during the inward stroke of said power piston, said venting port being covered by said striker member after said power piston has begun its outward stroke.

11. In the rotary-hammer device recited in claim l0, additional port means formed in said cylinder and open to atmosphere, said additional port means being spaced a slightly greater vdistance from the outer end of said cylinder than the longitudinal length of said striker member whereby to prevent the formation of a vacuum behind said striker member during inward movement of said power piston when said striker member advances into engagement with the outer end of the cylinder when no tool means projects into the outer end of the cylinder for impact engagement by said striker member.

12. in a power device adapted for imparting a hammerlike action to a tool element mounted therein, a cylinder, a power piston reciprocal in the rear end thereof, ra long shank tool element mounted in said device with the shank end thereof extending into the front end of said cylinder, exhaust port means at the front end of said cylinder opening to atmosphere, a piston-like striker member pneumatically reciprocal in said cylinder for impact engagement with the shank end of said tool element whereby to impart a hammer-like -action to .the tool element, the rearward stroke of said striker member being initiated by a vacuum of less than atmospheric pressure being created rearwardly thereof during rearward movement of said piston with the rearward movement ot said striker member continuing after said piston `has started its forward stroke whereupon lthe air disposed therebetween is compressed and serves to initiate a forward stroke of said striker member into impact engagement with the shank end of the long shank tool element, the air disposed forwardly of said striker member being evacuated to atmosphere through said exhaust ports during the forward stroke of said striker member, the rear face of said striker member when lin lits rearwardmost position after said piston has begun its forward stroke being disposed rearwardly of :the forwardmost position of the front face of said piston whereby there is lan area of overlap in the strokes et' said piston and said striker member, and a small vent port open to atmosphere formed in `said cylinder adjacent to and forwardly of said area of overlap, said vent port being open during the rearward stroke of said piston whereby zto permit suicient air to be drawn into the space between said piston and said striker member to compensate for any air leakage past said striker member and said piston during the forward power stroke of said striker member and thus prevent the development of a vacuum interlock between said piston and said striker member, said vent port being covered by said striker member during the period said striker member is disposed in said area of overlap after said piston has begun its forward stroke whereby a maximum compression torce is deveioped between said piston and said striker member to initiate a powerful forward stroke for said striker member.

13. In the power device recited in claim 12, means mounting said cylinder in which said piston and said striker member are wholly reciprocal for rotation about the longitudinal axis thereof, tool element driving means mounted in the forward end of said cylinder and disposed in rotary driving engagement with the shank of the tool element extending into said cylinder, and means for rotating said cylinder simultaneously during reciprocation of said piston and striker member therein whereby the tool element has a combination rotary and hammer-like action imparted thereto.

References Cited in the tile of this patent UNTTED STATES PATENTS 834,441 Adams Oct. 30, 1906 879,828 Proctor Feb. 18, 1908 974,267 Hennessey etal Nov. 1, 1910 1,072,359 Palmros Sept. 2, 1913 1,358,303 Farmer Nov. 9, 1920 1,461,460 Schroth et -al July 10, 1923 1,827,877 Meeker et al Oct. 20, 1931 2,343,137 Douglas Feb. 29, 1944 

1. IN A POWER HAMMER DEVICE, A CYLINDER HAVING A POWER PISTON RECIPROCAL IN ONE END THEREOF AND A WORKING TOOL ELEMENT ATTACHED TO THE OPPOSITE END THEREOF, SAID CYLINDER HAVING EXHAUST PORT MEANS IN SAID OPPOSITE END THEREOF, A FREE PISTON IN SAID CYLINDER ADAPTED TO IMPART A HAMMER-LIKE ACTION TO SAID WORKING TOOL ELEMENT, WHICH FREE PISTON IS ADAPTED TO BE PNEUMATICALLY RECIPROCATED DURING RECIPROCATION OF SAID POWER PISTON DUE TO THE ALTERNATE DEVELOPMENT OF HIGH AND LOW PRESSURES IN THE SPACE BETWEEN SAID PISTONS DURING RESPECTIVE INWARD AND OUTWARD STROKES OF SAID POWER PISTON RELATIVE TO SAID CYLINDER, SAID CYLINDER HAVING A RELATIVELY SMALL VENT PORT FORMED IN THE WALL THEREOF ADJACENT TO AND INWARDLY OF THE INNERMOST POSITION OF SAID POWER PISTON, SAID VENT PORT BEING OPEN TO ATMOSPHERE TO PREVENT THE CREATION OF A VACUUM INTERLOCK BETWEEN SAID PISTONS BY PERMITTING, DURING THE OUTWARD STROKE OF SAID POWER PISTON, THE INTAKE OF SUFFICIENT AIR INTO THE SPACE BETWEEN SAID PISTONS TO COMPENSATE FOR ANY AIR LOST PAST SAID FREE PISTON DURING THE INWARD STROKE OF SAID POWER PISTON, SAID VENTING PORT BEING CLOSED FROM THE ATMOSPHERE BY SAID FREE PISTON ONLY AFTER SAID POWER PISTON HAS STARTED ITS INWARD STROKE WHEREBY TO PERMIT THE DEVELOPMENT OF A FINAL MAXIMUM COMPRESSION FORCE BETWEEN SAID POWER AND FREE PISTONS. 